Cat-back vs muffler

[Inspector13]

My piping was 2.25 inches OD. The muffler I got was a 2.25 ID glasspack and slipped (snugly) over the factory piping. I will try answering your questions to the best of my abilities. Most of my experience/knowledge is with older V8's with carburetors and Chevrolets (I'm now taking a crack at fuel injected Ford V8's).

Q1. Depends on the application. My old Silverado the factory manifolds flowed just as much air as any available aftermarket shorty headers (at the time and I don't know if that has changed), and the cats flowed pretty good as well. Cat-backs on stock~ish vehicles will add power but not very much, where they do come into play is on more modified vehicles, but they do change the sound which is why most people buy them. Replacing just the muffler will add some power as well but not as much as changing the piping too (I might pick up another .5 mpg and maybe 2 or 3 more hp replacing the piping with larger mandrel bent stuff on my V6 as opposed to the factory stuff I got now). A V8 explorer could probably get more power doing the same mods as a V6 explorer due to the larger amount of air that could be moved by the larger engine. The factory cat-back is a restriction (which is why I asked because I am not super familiar with explorers and didn't know how restrictive it was compared to the rest of the exhaust). Replacing a restrictive cat-back with a free flowing aftermarket one will lessen 1 of the 3 restrictions in the exhaust.

Q2. Motors (four stroke) don't necessarily need back pressure (two stroke motors do). Running straight pipes from the manifolds back will make the vehicle obnoxiously loud (& IMO shitty sounding). I've found that you also lose a bit of low end torque & throttle response from my experience with it on my Escort, but maybe it was just my Escort.

Q3. If your just looking for just sound then just a muffler would probably be your best bet. An entire cat-back would net more power but if that isn't what your looking for I'd personally say save your money.

Q4. Isn't conduit tubing ribbed?? If so then that is bad as the ribs will restrict air flow more then the stock piping probably would. I'd stay away from the flex pipe stuff as well as I've had bad experience with them leaking and rusting out. I welded up my own exhaust on my Nova out of stainless steel. If you have a cutter & welder and some time and patience you very well could make your own exhaust. IMHO 3 inch may be a bit much for a V6 (even stock~ish V8's) as the added weight of the larger piping would out weigh (literately) the power added from the additional air flow from the larger piping (as you said the manifolds/cats would restrict the exhaust).

[College Student]

Alright very informative. As for the conduit it is not ribbed. If it were it would make pulling this 12500 feet of #10 much harder. The only difference i can fully see between this of conduit say 2.75in diameter (so i can basically have 2.5in ID) would be material and maybe a wall thickness, but it isnt much. I've welded the conduit for a previous project and it worked well. Bending is very easy with the correct benders. The hardest would be bending a 90 then bending a 75 ish from the midde of that bend to make the axle hoop.

[Inspector13]

What is it made out of??? Steel?? Aluminum??

[College Student]

It's steel but from looking up prices it will be cheaper to use http://www.summitracing.com/parts/FLO-15901/ or piece together a kit then to buy the cat back system saving me nearly $300

[badloser]

Originally Posted by HiImBrian

Nobody gets better mileage from upgrading their exhaust. Pedals hit the floor a lot faster when it sounds good.

good piont!!!!!

[doug625]

a less restrictive exhaust can improve mileage, it's just that we might like the sound better so we are hitting the pedal a little harder...and from my experience, a less restrictive exhaust system will help MPG's more on highway driving, and in some cases it can hurt mileage in town because of less back pressure.....ever drive a car with open headers? no low end power....you need a certain amount of back pressure(especially at lower rpm's) or you can actually lose some torque until getting to higher rpm's. Every setup is unique, but think of the engine as a big air pump. The easier air gets in and out, the better it will run, and in most cases this means the harder we will drive.

[desertsky]

Originally Posted by College Student

Alright very informative. As for the conduit it is not ribbed. If it were it would make pulling this 12500 feet of #10 much harder. The only difference i can fully see between this of conduit say 2.75in diameter (so i can basically have 2.5in ID) would be material and maybe a wall thickness, but it isnt much. I've welded the conduit for a previous project and it worked well. Bending is very easy with the correct benders. The hardest would be bending a 90 then bending a 75 ish from the midde of that bend to make the axle hoop.

Another main difference is the material conduit is made from is not designed to have 1000 degrees of hot, corrosive exhaust travelling through it. It would not last very long.